Blacklisting your own domain?

After having yet another user fall for a phishing scam and giving their user/pass
out to spammers, and the ensuing headaches (delistings, temporary re-routings,
etc), I'm decided to try something really simple in SpamAssassin:

blacklist_from          *@pil.net

I'm trying to think how this might cause problems, but I can't think of any. 
Users that SMTP Auth or POP Before SMTP bypass SA.  Is this fairly common practice
already?  Am I that slow to the game?
-- 
Eat sushi frequently. - Avi
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